In recent years, UV light is often used for cleaning of glass substrates and for various photochemical reactions. Low-pressure mercury lamp and excimer lamps are often used as UV light source. These lamps have strong spectrum near specific wavelength. UV light of the specific wavelength causes various chemical reactions to dissolve and reform the irradiated materials. Low-pressure mercury lamps emit fixed wavelengths at 185 nm and 254 nm. Excimer lamps emit several different wavelengths but cannot emit arbitrary wavelength. Also, it cannot emit in arbitrary wavelength region and wavelength width. And also, it cannot be applied to the field of irradiation with wide-range wavelength.
A deuterium lamp is well known as a lamp to have continuous spectrum from vacuum UV to UV range. Especially, it is used widely for scientific instruments. There are some examples as disclosed in the non-patent document 1 and the patent document 1. Their structure is as follows. A metal shield box with a pinhole is furnished in a discharge vessel with a window to transmit UV light. The shield box is an entirely isolated space except through the pinhole. An anode is disposed in the shield box and a cathode is disposed outside of the shield box. Discharge arises between the anode and the cathode through the pinhole at lighting time and the positive column of discharge is squeezed by the pinhole. Intense continuous spectrum UV light is emitted from the constricted portion of discharge.
The lamp as disclosed in the patent document 1 is a long-life deuterium lamp with improved characteristics of heat radiating from anode. An anode and a cathode are furnished in a glass discharge envelope filled with gas. Electrical leads are connected to the anode and the cathode respectively hermetically passing through the discharge envelope. And also, the lamp has a window shield electrode, a cathode shield electrode, a focusing electrode and a ceramic support. The anode is mounted on the backside of the ceramic support. The heat radiation from the anode to backward is improved. The patent document 2 discloses an industrial deuterium lamp with plural radiating points of about 1 mm in diameter in the tubular lamp.    [Patent document 1] JP2001-015073A    [Patent document 2] JPH01-137554A    [Non-patent document 1] MURAYAMA Seiichi: “The Characteristics of Light Source and its Usage,” Measuring Method Series 9 of The Spectroscopical Society of Japan, pp. 23-30, Japan Scientific Societies Press, 1985.